In modern society, over the past fifty years, there has been a shift from metals to polymers, partly because the latter do not oxidize in the environment. For example, corrosion of metal destroys valuable property. Corrosion is the inevitable reaction of metal to form metal oxide when the metal is exposed to environmental conditions that permit such corrosion. Billions of dollars are spent each year to repair or replace metallic structures because of such corrosion.
The corrosion of iron-containing articles, the natural process normally called “rusting”, has prompted considerable effort to find effective, economical ways to prevent or reduce rust. Coating the surface of the iron-containing article, the process of painting, was first attempted to shield the article from the elements needed for the natural rusting reaction to begin.
Iron-containing articles form the structures that have erected the cities and commercial links between them. Ironwork, for such diverse uses as multi-story buildings, suspension bridges, tunnels beneath a mountain or a river, high tension utility powerlines, fuel storage tanks, the Statue of Liberty, the Eiffel Tower, and reinforcement grids for concrete structures of all types, all require such protection from corrosion.
Anti-corrosion mechanisms have taken advantage of the Galvanic Series, whereby a less noble metal is a sacrificed in the environment where the iron would otherwise rust. This “cathodic protection” of metal has spawned an enormous industry dedicated to preserving metallic property against the ravages of the environment.
Cathodic protection utilizes the physics of a galvanic circuit, which can be assisted by power to be an active circuit to drive the corroding effects away from the metal being protected or which can be passive without power. Examples of passive galvanic circuitry are disclosed in U.S. Pat. No. 5,650,060 (Huang et al.) for an electrode-based system and in U.S. Pat. No. 5,976,419 (Hawkins et al.) for a coating-based system. Both types of systems rely on a more anodic metal in the Galvanic Series, such as zinc, to protect the more valuable iron in the structure. In the Huang et al. electrode, the zinc is in the form of plate adhered by an ionically conductive adhesive to a structure. In the Hawkins et al. coating, the zinc is in the form of particles dispersed in the binder and inherently conductive polymer. In both cases, the zinc is the anode of the galvanic circuit. The anodic zinc is sacrificed to preserve the cathodic iron.
U.S. Pat. No. 5,700,398 (Angelopoulos et al.) discloses a polymeric matrix with a conductive filler comprising conductive particles and an inherently conductive polymer which are useful for corrosion protection layers for metal substrates and other purposes.
U.S. Pat. No. 5,098,771 (Friend) discloses a fibril filled electrically conductive composite that can form a coating of sufficient electrical conductivity to be used in combination with sacrificial anode materials on the exposed surface of a metal or molded plastic part to help prevent corrosion.
U.S. Published Patent Application 20030122111 (Glatkowski) discloses an electrically conductive film having a plurality of nanotubes and optionally an additional conductive material.